It is commonly known that rats love to use the sewer network as a travel system which means it is entirely possible they are running through or nesting in the drainage under your house and garden. As they are very flexible and determined, they can easily leave the pipework through any rodding accesses that have missing caps or open points such as a break in the drain, letting them burrow out and run around the space under the floorboards. Another point of escape is through a gully in your garden if it does not have a trap at the base. They can also climb up the vertical pipes and it is not unusual for them to be in loft areas and cavity walls.
There are 3 possible methods of physical defence against rats entering the private drainage system which are as below. It is unlikely that the Local Water Authority will agree to have any of these installed in their assets due to potential blockages with the higher level of use of the pipework as these drains serve a number of properties and the need for regular maintenance for some of the methods.
Interceptor traps are usually found in the outlet of the last manhole chamber and this is the favoured design to prevent the passage of vermin from the communal sewers as rats are very unlikely to swim through the water holding in the U-bend of the trap. These have a rodding access which usually allows a blockage to be cleared with ease and the cap should always be in place to stop rats escaping from this point.
Marine Grade Steel Rat Blocker
These one-way metal flaps allow waste to flow downstream but will not open the opposite direction, preventing rats from passing. They have sharp edges which rats will not try to squeeze past and the strong material means the rats cannot chew their way through.
This is a cheaper option compared to the interceptor trap however these do require annual maintenance to ensure the hinge is operating satisfactorily and are more likely to cause blockages especially if non-disposables are let into the system.
These should be positioned in the same place as the interceptor trap.
Water and Rodent (WAR) Valve
Similar to rat blockers as they also have a one-way flap, these smaller valves are best used in the branch connections in the manhole chamber if the installation of an interceptor trap or rat blocker is not possible, such as the main run is a Local Water Authority asset. In our opinion, these are not the best option as rats can chew through the plastic components, allowing them to bypass the stainless steel flap. These need to be inserted into each private branch connection in the manhole so rats can only travel through the communal drain.
Please note that when any of the above have been installed, any rats located in the private system will no longer be able to escape to the main sewer and will effectively be trapped in the system. It is likely that the rats will attempt to escape via any other routes possible and we, therefore, recommend that a pest control company attends on the day after installation to exterminate the rats which may then die within the drainage system.
Another good preventative measure is to seal any redundant drains with cement at the chamber as they like to nest in the dry sections of pipework that are no longer in use.
If you are unsure if your drainage has any defence against rats, we can attend to assess the system as well as carry out a CCTV drain survey to check the condition to see if there are any signs of rat activity or possible escape points. Once we have inspected the system, we can provide you with a quote to install some form of defence and repair any defects found.
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